1 files changed, 28 insertions, 0 deletions
diff --git a/test/functional/rpc_fundrawtransaction.py b/test/functional/rpc_fundrawtransaction.py
index fcc310394a..bbd3dbb10c 100755
--- a/test/functional/rpc_fundrawtransaction.py
+++ b/test/functional/rpc_fundrawtransaction.py
@@ -100,6 +100,7 @@ class RawTransactionsTest(BitcoinTestFramework):
         self.test_transaction_too_large()
         self.test_include_unsafe()
         self.test_22670()
+        self.test_feerate_rounding()
 
     def test_change_position(self):
         """Ensure setting changePosition in fundraw with an exact match is handled properly."""
@@ -1026,6 +1027,33 @@ class RawTransactionsTest(BitcoinTestFramework):
         do_fund_send(upper_bound)
 
         self.restart_node(0)
+        self.connect_nodes(0, 1)
+        self.connect_nodes(0, 2)
+        self.connect_nodes(0, 3)
+
+    def test_feerate_rounding(self):
+        self.log.info("Test that rounding of GetFee does not result in an assertion")
+
+        self.nodes[1].createwallet("roundtest")
+        w = self.nodes[1].get_wallet_rpc("roundtest")
+
+        addr = w.getnewaddress(address_type="bech32")
+        self.nodes[0].sendtoaddress(addr, 1)
+        self.nodes[0].generate(1)
+        self.sync_all()
+
+        # A P2WPKH input costs 68 vbytes; With a single P2WPKH output, the rest of the tx is 42 vbytes for a total of 110 vbytes.
+        # At a feerate of 1.85 sat/vb, the input will need a fee of 125.8 sats and the rest 77.7 sats
+        # The entire tx fee should be 203.5 sats.
+        # Coin selection rounds the fee individually instead of at the end (due to how CFeeRate::GetFee works).
+        # If rounding down (which is the incorrect behavior), then the calculated fee will be 125 + 77 = 202.
+        # If rounding up, then the calculated fee will be 126 + 78 = 204.
+        # In the former case, the calculated needed fee is higher than the actual fee being paid, so an assertion is reached
+        # To test this does not happen, we subtract 202 sats from the input value. If working correctly, this should
+        # fail with insufficient funds rather than bitcoind asserting.
+        rawtx = w.createrawtransaction(inputs=[], outputs=[{self.nodes[0].getnewaddress(address_type="bech32"): 1 - 0.00000202}])
+        assert_raises_rpc_error(-4, "Insufficient funds", w.fundrawtransaction, rawtx, {"fee_rate": 1.85})
+
 
 if __name__ == '__main__':
     RawTransactionsTest().main()